Pteridinone derivatives are known from the prior art as active substances with an antiproliferative activity. WO 03/020722 describes the use of dihydropteridinone derivatives for the treatment of tumoral diseases and processes for preparing them.
7,8-Dihydro-5H-pteridin-6-one derivatives of formula (I) are important intermediate products in the synthesis of these active substances. Up till now they have been prepared using methods involving reduction of nitro compounds of formula (II) below, which led to strongly coloured product mixtures and required laborious working up and purification processes.
WO 96/36597 describes the catalytic hydrogenation of nitro compounds using noble metal catalysts with the addition of a vanadium compound, while disclosing as end products free amines, but no lactams.
The aim of the present invention is to provide an improved process for preparing compounds of formula (I), particularly 7,8-dihydro-5H-pteridin-6-one derivatives.